A STUDY OF PSEUDO-1-D COPPER(I) HALIDE-SYSTEMS EXHIBITING ANOMALOUS COPPER(II) CHARACTER - PHYSICAL CHARACTERIZATION OF (PARAQUAT)CU(2)X(4)(X=CL, BR, I)

The salts (paraquat) Cu(2)X(4) (X = Cl, Br, I) have been synthesized a nd their crystal structures determined. The chloride salt is tetragona l, space group P4(2)/n, a = 16.352(2), c = 5.911(2) Angstrom, V = 1580 .7(6) Angstrom(3), D-x = 1.87 g cm(-3), Z = 4 and R = 0.0546. The brom ide analog is monoclinic, space group P2(1)/n, a = 8.715(6), b = 11.10 3(6), c = 13.386(7) Angstrom, beta = 98.02(4)degrees, V = 1666(1) Angs trom(3), D-x = 2.52 g cm(-3), Z = 4 and R = 0.0680. The iodide salt is tetragonal, space group P4(2)2(1)2, a = 12.416(2), c = 6.544(3) Angst rom, V = 1008.8(5) Angstrom(3), D-x = 2.70 g cm(-3), Z = 2 and R = 0.0 995. Infinite chains of distorted, edge sharing, Cu(I)X(4)(3-) tetrahe dra are common to all three structures. The bond distances and angles about the copper centers are consistent with known Cu(I)X(4)(3-) speci es. The paraquat cations form stacks parallel to the chain axis, and a ll three structures show weak N ... X and C ... X contacts. The chlori de and iodide salts are nearly isostructural, and differential scannin g calorimetry shows a phase transition in the chloride salt at 188 deg rees C. The iodide salt is a pure copper(I) system. A temperature depe ndent magnetic susceptibility experiment shows the bromide salt to con tain a 2% Cu2Br62- impurity. Two chloride compounds showing the same s tructure have been synthesized. One of these salts has 1% copper(II) c haracter, while the other has 10% copper(II) character. EPR shows the 1% character to be a CuCl2 . 2H(2)O impurity. Magnetic susceptibility, EPR, powder diffraction and electrical conductivity results show that the 10% copper(II) character is incorporated into the [CuC2](infinity ) chain structure, with an accompanying vacancy. Preliminary conductiv ity measurements show that the Cl and I salts are insulators, but hint at enhanced conductivity for the bromide analog.